This research is broadly concerned with determining basic principles of how the nervous system develops and with defining the prinicipal dimensions of neural ontogeny affected by different genotypes within the same species. Specifically, we are analyzing the embryonic spinal cords of different inbred strains of mice in order to define developmental similarities and differences in the formation of the neuronal connections which comprise the cutaneous reflex arc. We are employing reflex behavioral testing, tritiated thymidine radioautography and a variety of neuroanatomical methods in this research. It is anticipated that these studies will contribute toward both an understanding of normal brain development and the neuroembryological process regulated by genes. It is hoped that such knowledge will be useful for investigations of cases where genetically-associated abnormalities of brain development are the suspected basis of adult brain disorders.